/Engine/Source/Editor/DataLayerEditor/Public/DataLayer/DataLayerEditorSubsystem.h
Changes the DataLayer's IsLoadedInEditor flag to the provided state
bool SetDataLayerIsLoadedInEditor ( [UDataLayerInstance](API\Runtime\Engine\WorldPartition\DataLayer\UDataLayerInstance) * DataLayer, const bool bIsLoadedInEditor, const bool bIsFromUserChange )